Process for separating benzene hexachloride isomers



Patented Apr. 6, 1948 PROCESS FOR SEPABATING BENZENE HEXACHLORIDE ISOMERS William Herbert Cooke, Liverpool, and James Crosby Smart, Widnes, England,

assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing.

This invention relates to improvements in the production of mixtures containing benzene hexachloride, and to pest control compositions containing such mixtures.

It is known that mixtures of isomeric benzene hexachlorides can be obtained by reacting chlorine with benzene under conditions promoting addition of chlorine, but not the substitution of chlorine for hydrogen; after removing any unchanged benzene a solid mixture of isomers remains in which the a-isomer, M. P. 158 C. predominates. The s-isomer, M. P. 305 C., and the 'y-isomer, M. P. 113 C., are also present. Such a mixture of isomers in which the a-iSOmBI predominates is conveniently referred to as crude benzene hexachloride. The chlorination step may be carried out at ordinary or elevated temperature, and either discontinued while all of the isomers are still in solution in unchanged benzene, or it may be continued until solid a-benzene hexachloride separates. In either case the unchanged benzene can then be removed conveniently by contacting the slurry or solution with hot water. In the copending application of Burrage and Smart, Serial No. 537,372, filed May 25, 1944, there is described the isolation of 'y-isomer or mixtures containing an enhanced proportion thereof from a crude benzene hexachloride by extracting the crude benzene hexachloride in the cold with a lower aliphatic alcohol, preferably methanol or ethanol. The a-isomer has but a small solubility in the lower aliphatic alcohol compared with the 'y-isomer, and thus a separation can be efiected.

We have now found that for other aliphatic compounds, and for cycloaliphatic compounds containing S-carbon atom rings, which are solvents for the benzene hexachlorides, similar solubility relationships exists between the 'y-isomer and the a-isomer, so that by extracting the additive chlorination product of benzene with such a solvent, after removing unchanged benzene, it is possible to produce a solution of isomeric benzene hexachiorides containing an enhanced proportion of 'y-isomer to a-isomer.

According to the present invention, therefore, a process for treating crude benzene hexachloride to obtain a mixture of isomers containing an enhanced proportion of the 'Y-isomer comprises extracting it with an aliphatic solvent therefor Application April 2, 1945, Serial In Great Britain April 3, 1944 13 Claims. (Cl. 260-648) (other than a lower aliphatic alcohol), or with a cycloaliphatic solvent therefor containing a 6- carbon atom ring, such an amount of solvent being employed as to dissolve 'y-isolner and leave a substantial proportion of the a-isomer undissolved.

Advantageously the amount of the solvent used to carry out the extraction is not significantly greater than that required to dissolve substantialiy all of the 'y-isomer. However, if the presence of some a-iSOmEI' is not objectionable, rather more of the solvent may be used and a corresponding proportion of the a-isomer Will then be present in the extract together with the 'y-isomer. Some fi-isomer may also'be present in solution. However, the amount of fi-isomer in the crude benzene hexachloride is small, and this isomer has a lower solubility than the a-iSOmGI in all the solvents which we have tried; on both accounts, therefore, the amount of p-isomer in the extract containing the 'y-isomer will be small. Minor proportions of chlorinated benzene hexachlorides, for example monochlorobenzene hexachloride, may be formed during the initial chlorination and these will then also be present in the solution, for they appear to have a greater solubility in most solvents than the 'y-isomer.

Suitable compounds which may be used as solvents for carrying out the extraction include normally liquid chlorinated hydrocarbons such as chloroform, carbon tetrachloride, cis-dichloroethylene, trans -dichloroethylene, trichloroethylene, perchloroethylene, and ethylene dichloride; esters such as methyl acetate, methyl propionate, methyl dichloroacetate, ethyl acetate, n-butyl acetate, diethyl carbonate; normally liquid hydrocarbons such as heavy naphtha, odourless distillate, kerosene, and petrol ether. Other aliphatic solvents which may be used include diacetone alcohol, dimethyl' acetal, carbon disulphide, ethyl ether, acetone, and glacial acetic acid. cycloaliphatic solvents containing 6-carbon atom rings which may be used include cyclohexane, cyclohexene, cyclohexanol, cyclohexvanone, and decahydronaphthalene.

The following table indicates the solubilities of the a-isomer and the 'y-isomer in these solvents at a temperature of 20 C. The solubilities are given as the number of parts of a or -isomer,

Solubility oi' Solvent wisomer 'y-isomcr Chlorinated alipathic hydrocarbons:

chloroform ethylidene chloride. porchloroet hylcne. ethylene dichloride. trichloroethylene Esters of alipathic carboxy methyl acetate ethyl acetate The amount oi. solvent selected to carry out the extraction in any form of the invention will depend on the solubility oi the 'y-isomer in that particular solvent at the temperature of extraction. The minimum will in any casevbe that which gives a mixture of solution and undissolved material from which it is practicable to separate the former, and this corresponds to approximately equal bulks of solvent and crude benzene hexachloride, although for the liquids with a low solvent power for the benzen hexachloride isomers it may be preferable to use at least 1.5 times this amount. Subject to this restriction the most advantageous amount of solvent will be the minimum which will dissolve all of the 'Y-isomer, and can be found by trial in any particular case. For practical purposes, when carrying out extraction in the cold with a solvent in the table aibove, an approximation to a suitable amount of solvent can be deduced by calculating, from the 'y-solubility figure, the minimum of solvent necessary to dissolve all the 7 present in a given amount of a mixture of isomers. It is understood, however, that the amounts of solvent to use, as given by this method, are approximate, and indeed the proportion of solvent to benzene hexachloride is not extremely critical. Nevertheless this method gives an indication of an amount of solvent which will give, for practical purposes, a useful result. Thus in extracting 100 parts 'by weight of crude benzene hexachloride containing 12% 'Y-isomer with trichloroethylene, 70yparts of solvent would be suitable, with decahydronaphthalene 125 parts would be appropriate, and with cyclohexane 250 parts. If the volume of the solvent selected in this way is less than the bulk occupied by 100 parts by weight of benzene hexachloride, it will be necessary in practice to use a greater amount, and only a product containing some a-isomer in addition to the -'y-isomer can be obtained. If the volume or the solvent so selected is greater than the bulk of the 100 parts of benzene hexachloride, less or more than this amount can also be used, and a product containing a correspondingly smaller or greater amount or. a-isomer will result. Thus in the case of carbon disulphide and glacial acetic acid, rather more than thisminimum amount can be used without dissolving large amounts of u-isomer. On these considerations it will be advantageous to employ a, solvent not capable of dissolving more than approximately 12 grms. of 'y-benzene hexachloride in 100 mls. oi solvent.

If it is desired to use a solvent with a greater solvent power than this th latter property may be diminished by the addition or a second liquid miscible therewith which has at most a low solvent power tor the benzene hexachloride isomers. Thus, glacial acetic acid may be diluted with up to 15% by weight of water, and acetone with up to 25% by weight of water. Similarly the chlorinated hydrocarbon solvents and the carboxylic ester solvents may be diluted with small amounts of a pentane or a petrol ether fraction.

It appears that, at least in some cases, the presence oi! the 'y-isomer in solution depresses the solubility of the a-isomer. It is then possible, by suitably selecting the proportion of solvent to benzene hexachloride, to obtain an extract containing a much greater ratio of w-isomer to aisomer than is indicated by consideration of the solubilities of the pure isomers in the solvent.

For many hydrocarbon solvents the absolute .solubilities are so low that they are not convenient to use in practice. On the contrary, some of those having but small solvent power may be used not only to depress the solvent power of more powerful solvents as described above, but also to precipitate at least a part of the dissolved material from solutions of benzene hexachloride in such solvents after carrying out the extraction with the latter. Thus petrol ether may be usedto effect precipitation, or partial precipitation, of benzene hexachlorides from a concentrated solution thereof in heavy naphtha or methanol.

In one method of carrying out our invention benzene is chlorinated under conditions which produce benzene hexachloride; suitably, chlorine is passed into a quantity of cold or warm benzene irradiated by sunlight, or the light from a mercury arc lamp. Chlorination is continued until a 15% to 20% solution of the isomeric benzene hexaehlorides in benzene is produced, though if desired, the chlorination may be carried further so that a slurry of benzene hexachloride results. The solution or slurry is then gradually added to a quantity of hot water, for example water at 75 C. to C., so that unchanged benzene is evaporated ofl, and the mixture of isomeric benzene hexachlorides is precipitated. This mixture is then dried in an air oven or otherwise, and roughly ground in any suitable manner. Such a product contains approximately 8% to 12% ot th 7-15011'181'. The ground material is then extracted in the cold with the selected cycloaliphatic or aliphatic solvent which may be, for example, trichloroethylcne, cyclohexane or decahydronaphthalene. The extraction may be carried out by stirring the solvent with the benzene hexachloride for a suitable time, for example for 1 to 2 hours. The resultant solution is then separated all the solvent. Thus a glacial acetic acid extract may be treated with water to precipitate all or part of the benzene hexachloride in solution, and extracts obtained 3 using carbon tetrachloride, chloroform, trichloroethylene or perchloroethylene may be similarly treated with a pentane, or a petrol ether fraction.

Other methods of carrying out the invention may be used. Th'us when a solvent is chosen in which the solubilities of the benzene hexachlorides are relatively high, for example chloroform or acetone, a solution may be made of the whole of the material in such an amount of hot solvent that the solution would be supersaturated in the cold, and the solution cooled so that a substantial amount of benzene hexachloride, which will be mainly the a-isomer, separates. After removing this solid a solution will then remain containing a mixture of isomers with a ratio of Y to an enhanced to an extent depending on the proportion of solvent taken.

Again, before carrying out the extraction, the crude benzene hexachloride may bewashed with a liquid which has a low solubility for the 'y-lSO- mer, such as petrol ether, in amount sumcient to remove the chlorinated benzene hexachlorides without dissolving any substantial amount of Y- isomer. An extract will then be obtained which is free from these impurities. This may be advantageous, for example, if it is desired to recover -isomer from the extract by fractional crystallisation, for these impurities mar the clean separationand crystalline nature of the fraction deposited from solution. Other liquids which may be used for this purpose instead of petrol ether include n-pentane, odourless distillate, ethylene glycol, and acetic acid containing to of water.

If desired, the crude benzene hexachloride may, before treating it with a solvent, be submitted to a deodorising treatment; thus it may be boiled with concentrated nitric acid as is described in copending British application No. 19,477/43, treated with nascent hydrogen as described in copending British application No. 3,434/45, or with silica gel or absorbent carbon as described in copending British applications Nos. 18,571/44, 3,437/45, and 3,438/45. Such preliminary treatment is very conveniently applied when the solvent extract containing the Y-isomer is to be used the production of sprays by dilution with another solvent or with further quantities of the same solvent as described below.

The extract obtained by any of the methods above described, or the mixture of isomers obtained from it which contain an enhanced proportion of the Y-isomer, as compared with the original material, may be employed in the production of pest control compositions as described in copending British application No. 10,459/42. Sprays suitable for pest control purposes may also be obtained by diluting the solution, obtained by extracting the crude benzene hexachloride with solvent according to this invention, with further quantities of the same solvent or with another solvent miscible therewith. Thus, for example, the extraction may be carried out by means of decahydronaphthalene and the solvent extract can be diluted with heavy naphtha or kerosene to provide sprays suitable for controlling flies or mosquitoes.

The following examples illustrate but do not limit the invention, all parts being parts by weight:

Example 1 Benzene was chlorinated by passing chlorine into it at 50 C. while irradiating it with a mercury arc lamp. When the amount of chlorine reacted corresponded to the formation of a 20% solution of benzene hexachlorides in benzene, chlorination was stopped and the solution was added gradually to hot water so as to evaporate oil the benzene. The mixture of benzene hexachlorides remaining was filtered off, dried, and ground. The product contained approximately 12% -y-benzene hexachloride.

parts of the ground product were stirred for a time in the cold with 312 parts of cyclohexane, and the solution was filtered. It contained 18 parts of solids, of which approximately 12 parts were 'Y-benzene hexachloride. By evaporating oil the cyclohexane from the solution, 18 parts of solids could thus be obtained containing 66% of Y-benzene hexachloride.

Example 2 Ground benzene hexachloride, obtained as in Example 1, was submitted to a deodorising treatment by contacting it with coarse silica gel for some hours, and then removing the silica gel by sieving. This method is described and claimed in copending British application No. 19,47'7/43. 100 parts of the deodorised material were stirred with parts of decah'ydronaphthalene and the solution was filtered. The solution contained 18 parts of solids of which 11.4 parts were Y-benzene hexachoride. By diluting the solution with 20 times its volume of kerosene a liquid was obtained suitable for use as a fly spray.

Example 3 100 parts of ground benzene hexachloride, obtained as in Example 1, were stirred in the cold with 60 parts of heavy naphtha and the solution was filtered. The solution contained 32.5 parts of solids, of which 12 parts were Y-isomer.

Example 4 60 parts of the ground benzene hexachloride obtained as in Example 1 were stirred for a time in the cold with 30 parts of trichloroethylene, and the solution filtered. It contained 15 parts of solids, of which approximately a third was estimated to be 'Y-benzene hexachloride. By evaporating ofi the trichloroethylene from the solution, 15 parts of solids could thus be obtained containing approximately 33% of r-benzene hexachloride.

Example 5 dried to give a material containing 21% 'y-benzene hexachloride.

Example 7 200 parts of crude benzene hexachloride, ob

tained as inExample 1, containing 12% of 'yisomer were stirred for an hour at room temperature with 100 parts of methyl acetate. The resultant slurry was filtered and 130 parts of filtrate were obtained. n evaporating the filtrate to dryness 57 parts or solid were obtained containing 42% of 'y-benzene hexachloride,

It will be apparent from the foregoing descrip--- tion that the process of our invention can be carried out using a very varied range of solvents, all

of which are aliphatic compounds (other than lower aliphatic alcohols) or cycloaliphatic compounds containing a 6-carbon atom ring. In the following claims these solvents are referred to as selective solvents, sincethey have the power of selectively recovering Y-benzenehexachloride y from the crude benzene hexachloride.

We claim:

l. A process for treating crude benzene hexachloride to obtain a mixture of isomers containing an enhanced proportion of the 'y-isomer, which comprises extracting the crude benzene hexachloride with an amount of a selective solvent taken from the class consistingot aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons, and cycloaliphatic hydrocarbons having a 6-carbon atom ring suihcientto dissolve -y -isomer and leave a substantial proportion of the aisomer undissolved, and separating the solid aisomer from the 'y-isomer-enriched solution.

2. A process according to claim 1 in which the selective solvent is a normally, liquid chlorinated aliphatic hydrocarbon.

3. A process according to claim 1 in which the selective solvent is decahydronaphthalene.

4. A process for treating crude benzene hexachloride to obtain a mixture of isomers containing an enhanced proportion of the 'y-isomer which comprises agitating the crude benzene hexachloride in the cold with a selective solvent taken from the class consisting of aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons, and cycloaliphatic hydrocarbons having a 6-carbon atom ring in amount sufllcient to form a slurry containing the iii-isomer in the solid state, and separating the liquid phase from the solid. 5. A process according to claim 4 in which the selective solvent is a normally liquid chlorinated aliphatic hydrocarbon.

6. A process according to claim 4 in which the selective solvent is decahydronaphthalene.

"I. A process for treating the additive chlorination product of benzene to obtain a mixture of isomers containing an enhanced proportion ot the 'y-isomer, which comprises the steps of removing unchanged benzene therefrom, and agitating the crude residue in the cold with a selective solvent taken from the class consisting of aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons, and cycloaliphatic hydrocarbons having a B-carbon atom ring in amount sufllcient to dissolve -y-isomer and to give a slurry containing solid a-benzene hexachloride, and separating the liquid phase from the solid.

8. A process according to claim 7 in which the selective solvent is a normally liquid chlorinated aliphatic hydrocarbon.

9. A process according to claim 'I in which the selective solvent is decahydronaphthalene.

10. A process for treating the additivechlorination product of benzene to obtain a mixture or isomers containing an enhanced proportion,

of the 'y-isomer which comprises the steps oi removing unchanged benzene therefrom, and agitating the crude residue in the cold with a selective solvent taken from the class consisting of allphatic hydrocarbons, chlorinated aliphatic hydrocarbons, and cycloaliphatic hydrocarbons having a 6-carbon atom ring in amount not significantly greater than that required to dissolve sub stantially all of the 'y-benzene hexachloride and enable the resultant solution to be separated from undissolved solid, and separating the liquid phase from the solid.

11. A process for treating crude benzene hexachloride to obtain a mixture 01' isomers containing an enhanced proportion of the -isomer,

which comprises extracting the crude benzene hexachloride with an amount of a selective solvent completely miscible with a second selective solvent in which said 'y-isomer is less soluble than in said first solvent sumcient to dissolve -y-isomer and leave a substantial proportion of the a-isomer undissolved, separating the extract from undissolved u-benzene hexachloride adding an amount of said second solvent suillcient to precipitate solid from said solution, and isolating the precipitate.

12. A process according to claim. 11 in which the first selective solvent is a normally liquid chlorinated aliphatic hydrocarbon.

13. A process according to claim 11 in which the first selective solvent is decahydronaphthalene.

WILLIAM HERBERT COOKE. JAMES CROSBY SMART.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 447,058 Great Britain May "I, 1936 Certificate of Correction Patent No. 2,438,900. April 6, 1948.

WILLIAM HERBERT COOKE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 8, in the table, first column thereof, under the heading Solvent for Chlorinated alipathic hydrocarbons read Chlorinated aliphatic hydrocarbons; line 15, for Esters of alipathic carboxylic acids read Esters of aliphatic carboxylic acids; and that the said Letters Patent should be read with these corrections therein that thesame may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of June, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,438,900. April 6, 1948.

WILLIAM HERBERT COOKE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 8, in the table, first column thereof, under the heading Solvent for Chlorinated alipathic hydrocarbons read Chlorinated aliphatic hydrocarbons; line 15, for Esters of alipathic carboxylic acids read Esters of aliphatic carboxylic acids; and that the said Letters Patent should be read with these corrections therein that thesame may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of June, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

